Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$151.45	13.234%	$171.4929	$171.49	$171.50	$171.50
Purchase #2	$167.97	4.708%	$175.878	$175.88	$175.90	$175.90
Purchase #3	$190.99	13.802%	$217.3504	$217.35	$217.35	$217.40
Purchase #4	$170.72	7.326%	$183.2269	$183.23	$183.25	$183.20
Purchase #5	$191.79	4.705%	$200.8137	$200.81	$200.80	$200.80
Purchase #6	$108.83	8.490%	$118.0697	$118.07	$118.05	$118.10
Purchase #7	$83.60	6.804%	$89.2881	$89.29	$89.30	$89.30
7 purchase totals =	$1,065.35		$1,156.1197	$1,156.12	$1,156.15	$1,156.20